Emulsions in Industry
Emulsions are common colloidal systems in many industrial products such as Food, Cosmetics, Pharmaceutical or Agrochemical preparations. They are often used to deliver functional molecules, or to create a certain texture or pleasure to the consumer. Oil-in-water emulsions are made of oil droplets which are dispersed in an aqueous continuous phase. The dispersed oil droplets are stabilised by hydrophilic surface active molecules which form a layer around the oil droplets. In order to disperse the oil phase into the continuous aqueous phase, homogenisers are used which enable to produce oil droplets in various size ranges (having a radius from ca 100 nm up to several hundreds of micrometers). The formation of the layer around the oil droplets during the homogenisation step renders the oil droplets kinetically stable against coalescence, flocculation or coagulation.
The surface active material used in oil-in-water based emulsion products can either be low molecular weight hydrophilic surfactants, such as polysorbates, lysolecithins etc, or polymers, such as proteins, e.g. gelatin or proteins from milk, soya, or polysaccharides, such as gum arabic or xanthan or particulated materials, such as silica particles, or mixtures thereof.
Oil-in-water emulsion based products are ubiquitous in—Food, Cosmetics, Pharmaceuticals or Agro-chemicals. Prominent oil-in-water emulsion-based food products are for instance milk, mayonnaise, salad dressings, or sauces. Prominent oil-in-water emulsion-based products used in the cosmetical or pharmaceutical Industry are lotions, creams, milks, pills, tablets etc. The oil droplets in such products are usually made of, for instance, triglycerides, diglycerides, waxes, fatty acid esters, fatty acids, alcohols, mineral oils, hydrocarbons, or other oily substances.
Emulsions are used either as a starting material, intermediate or final product or as an additive to a final product.
Emulsions for Delivery of Active Elements
One of the uses of emulsions in Industry is to deliver active compounds, such as, flavours, vitamins, antioxidants, neutraceuticals, phytochemicals, drugs, chemicals, etc. Administrating of the active components requires the use of an appropriate vehicle for bringing an effective amount of the active component into the desired place of action. Oil-in-water emulsions are commonly used delivery systems since they take advantage of the increased solubility of lipophilic active compounds in the oil. In EP 1116515, as an example of using emulsions for controlling flavour performance, a hydrophobic active ingredient, such as a flavour component, is mixed into a matrix via an extruder in form of an oil-in-water emulsion in order to increase the stability of the introduced active ingredient during further processing of the product. In WO 00/59475, as an example for a pharmaceutical oil-in-water emulsion, a composition and method for improved delivery of ionizable hydrophobic therapeutic agents is described, which are mixed together with an ionizing agent, a surfactant and a triglyceride to form an oil-in-water emulsion. WO 99/63841, as an example for the use of emulsions in the food area, describes compositions comprising phytosterol having enhanced solubility and dispersibility in an aqueous phase due to the formation of an emulsion or a microemulsion.
Dissolution of active elements, such as phytosterols, lycopene or water-insoluble drugs into the oil droplets of o/w emulsions or dispersions cannot only facilitate the dispersibility, i.e. the homogeneous incorporation of the active elements into the product, but can also be used to increase their bioaccessibility or bioavailability. Clinical and animal experiments showed that the maximum efficiency and bioavailability of active elements, such as drugs and nutrients, is, in general, obtained when the active elements are solubilized or dissolved, for instance into micelles, and not present in the form of large crystals (Ostlund, E. O., C. A. Spilbourg, et al. (1999). “Sitostanol adminstered in lecithin micelles potently reduces cholesterol absorption in humans.” American Journal of Clinical Nutrition 70: 826-31; M. Kinoshita, K. Baba, et al. (2002). “Improvement of solubility and oral bioavailability of a poorly water-soluble drug, TAS-301, by its melt adsorption on a porous calcium silicate.” Journal of Pharmaceutical Sciences” 91(2): 362-370). Small or micronized crystals are more likely to be bioavailable than large ones since they will faster dissolve during digestion.
If the oil droplets in the oil-in-water emulsions are ultra small, e.g. in the order of several nanometers to about 200 nm diameter, the emulsion is called oil-in-water microemulsion (Evans, D. F.; Wennerström, H. (Eds.); ‘The Colloidal Domain’, Wiley-VCH, New York, (1999)). These emulsions are clear and thermodynamically stable and, therefore, are for the man skilled in the art different from ordinary emulsions the latter being thermodynamically unstable and generally turbid.